n 1  :  any of the electromagnetic radiations of the same nature as visible radiation but of an extremely short wavelength less than 100 angstroms that is produced by bombarding a metallic target with fast electrons in vacuum or by transition of atoms to lower energy states and that has the properties of ionizing a gas upon passage through it, of penetrating various thicknesses of all solids, of producing secondary radiations by impinging on material bodies, of acting on photographic films and plates as light does, and of causing fluorescent screens to emit light - called also roentgen ray   2  :  a photograph obtained by use of X rays <a chest X ray>  X-ray adj 
 
 
 
Similar sounding terms:  CER  cere  sera   sire 
 
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